The present invention relates to firearms.
In particular, the present invention relates to firearms such as semi-automatic shotguns, wherein upon firing of a round the gas pressure created is utilized for automatic operation of components of the firearm.
Thus, the present invention relates to firearms, in particular firearms such as semi-automatic shotguns, where a gas piston-and-cylinder assembly is provided with a pressure equalizing valve, the gas piston being mounted in a gas cylinder connected to the underside of the barrel of the firearm with the piston-and-cylinder assembly forming a continuation of a magazine tube which extends beneath the barrel, and the cylinder communicating at its front end region through a suitable gas passage with the interior of the barrel to receive gas under pressure therefrom when a round is fired.
It is known to provide for a semi-automatic shotgun an arrangement where the gas piston directly surrounds the magazine tube of the firearm. Through this expedient it is possible for the magazine to have a large capacity which, in the case of a semi-automatic shotgun, may be, for example, four cartridges. However, this type of construction has the disadvantage of requiring that the firearm have an objectionably great transverse dimension or thickness at the front butt region.
Also, there are known constructions where the gas piston and the cylinder in which it slides are arranged so as to form a continuation of the magazine tube with the gas piston reciprocating on the neck of a special solid rod which forms a continuation of the magazine tube. This type of construction requires an undesirably long space, considered longitudinally of the firearm.
In addition, it is extemely difficult in both of the above types of construction to accommodate a pressure relief valve which serves to equalize variations in pressure resulting from charges of different strengths. Thus, if an excessively strong charge is fired, the automatically operable structure of the gun will be driven with a force which is too strong, and a pressure relief valve is provided to avoid this undesirable operation.